Squid is not classified as a shellfish like shrimp but is rather a cephalopod in the order of Teuthida which contains about 300 different species. Squid have very distinctly triangle-shaped heads and bilateral symmetry which is part of what sets them apart from other sea organisms. They also tend to have fairly long tentacles and are very strong swimmers, able to almost fly short brief distances out of the water.
Squid is a very popular commercial type of seafood which is served at a number of restaurants all over the world and is very profitable with regards to the fishing industry. Squid are almost always caught in the wild and they are considered to be very difficult to farm.